Differentiating the Effects of Oxidative Stress Tests on Biopharmaceuticals.

PURPOSE: A rapid and broadly applicable method to assess relevant oxidative damage in biopharmaceuticals is important for lifecycle management of product quality. Multiple methods are currently employed as stress tests to induce oxidative damage for assessment of stability, safety, and efficacy. We compared two common methods for inducing oxidative damage to assess differences in impact on bioactivity and structure of the biopharmaceuticals. METHODS: Biopharmaceuticals were treated with either metal-catalyzed oxidation (MCO) conditions or the reactive-oxygen species (ROS) inducer 2,2'-Azobis(2-amidinopropane) dihydrochloride (AAPH), then analyzed for changes in structure and bioactivity. RESULTS: We demonstrate that commonly used chemical methods for assessing oxidation yield distinct oxidation profiles for each of the biotechnology products analyzed, including monoclonal antibodies. We further report oxidant- and product-specific changes in bioactivity under oxidizing conditions, along with differential oxidation on the molecular subunits of monoclonal antibodies. CONCLUSION: Our results highlight the need for product-specific optimization and selection of orthogonal, relevant oxidizers when characterizing stress responses in biopharmaceuticals.

Correction to: The Asp99-Arg188 salt bridge of the Pseudomonas aeruginosa HemO is critical in allowing conformational flexibility during catalysis.

In the original publication, fifth author's name was incorrectly published as Pierre Moenne-Loccoz.

The Asp99-Arg188 salt bridge of the Pseudomonas aeruginosa HemO is critical in allowing conformational flexibility during catalysis.

The P. aeruginosa iron-regulated heme oxygenase (HemO) is required within the host for the utilization of heme as an iron source. As iron is essential for survival and virulence, HemO represents a novel antimicrobial target. We recently characterized small molecule inhibitors that bind to an allosteric site distant from the heme pocket, and further proposed binding at this site disrupts a nearby salt bridge between D99 and R188. Herein, through a combination of site-directed mutagenesis and hydrogen-deuterium exchange mass spectrometry (HDX-MS), we determined that the disruption of the D99-R188 salt bridge leads to significant decrease in conformational flexibility within the distal and proximal helices that form the heme-binding site. The RR spectra of the resting state Fe(III) and reduced Fe(II)-deoxy heme-HemO D99A, R188A and D99/R188A complexes are virtually identical to those of wild-type HemO, indicating no significant change in the heme environment. Furthermore, mutation of D99 or R188 leads to a modest decrease in the stability of the Fe(II)-O2 heme complex. Despite this slight difference in Fe(II)-O2 stability, we observe complete loss of enzymatic activity. We conclude the loss of activity is a result of decreased conformational flexibility in helices previously shown to be critical in accommodating variation in the distal ligand and the resulting chemical intermediates generated during catalysis. Furthermore, this newly identified allosteric binding site on HemO represents a novel alternative drug-design strategy to that of competitive inhibition at the active site or via direct coordination of ligands to the heme iron.

Iminoguanidines as Allosteric Inhibitors of the Iron-Regulated Heme Oxygenase (HemO) of Pseudomonas aeruginosa.

New therapeutic targets are required to combat multidrug resistant infections, such as the iron-regulated heme oxygenase (HemO) of Pseudomonas aeruginosa, due to links between iron and virulence and dependence on heme as an iron source during infection. Herein we report the synthesis and activity of a series of iminoguanidine-based inhibitors of HemO. Compound 23 showed a binding affinity of 5.7 µM and an MIC50 of 52.3 µg/mL against P. aeruginosa PAO1. An in cellulo activity assay was developed by coupling HemO activity to a biliverdin-IXα-dependent infrared fluorescent protein, in which compound 23 showed an EC50 of 11.3 µM. The compounds showed increased activity against clinical isolates of P. aeruginosa, further confirming the target pathway. This class of inhibitors acts by binding to an allosteric site; the novel binding site is proposed in silico and supported by saturation transfer difference (STD) NMR as well as by hydrogen exchange mass spectrometry (HXMS).

Small molecule antivirulents targeting the iron-regulated heme oxygenase (HemO) of P. aeruginosa.

Bacteria require iron for survival and virulence and employ several mechanisms including utilization of the host heme containing proteins. The final step in releasing iron is the oxidative cleavage of heme by HemO. A recent computer aided drug design (CADD) study identified several inhibitors of the bacterial HemOs. Herein we report the near complete HN, N, CO, Cα, and Cß chemical shift assignment of the P. aeruginosa HemO in the absence and presence of inhibitors (E)-3-(4-(phenylamino)phenylcarbamoyl)acrylic acid (3) and (E)-N'-(4-(dimethylamino)benzylidene) diazenecarboximidhydrazide (5). The NMR data confirm that the inhibitors bind within the heme pocket of HemO consistent with in silico molecular dynamic simulations. Both inhibitors and the phenoxy derivative of 3 have activity against P. aeruginosa clinical isolates. Furthermore, 5 showed antimicrobial activity in the in vivo C. elegans curing assay. Thus, targeting virulence mechanisms required within the host is a viable antimicrobial strategy for the development of novel antivirulants.